Cavity wall

1. GENERAL

The principle of every cavity wall (leaving local differences in wall thickness and cavity width aside) looks as follows:

1. External cavity layer in stretching bond brickwork.
2. Cavity.
3. Internal cavity layer in bond or stretching bond brickwork.
4. Internal roughcast.

The function of a cavity wall is to avoid all water transfer to the inner leaf. Generally, the situation can be represented as follow:

- external cavity layer = umbrella
- cavity = capillary edge
- internal cavity layer + gypsum = airtightness

 It should be considered that during torrential rains, more or less water could run down from the external cavity layer after a shorter or longer lapse of time (according to the capillarity of the stone). This water should be drained away at the level of the cavity fixations.

A sound guarantee as for the rain tightness can not be given if:

• the inner cavity layer is extremely air permeable,
• the external cavity layer is erected from non-capillary stones,
• the cavity is (too) narrow.

The cavity can or cannot have extra ventilation. We can speak of extra ventilation as soon as under and above one or more butt joints are left open. During the construction the inner and outer cavity layer are linked together with wall ties (average 4 ties per m²).

We refer to the BUtgb information sheet "Insulated cavity walls with brick work outside" for a thorough discription of the Architectural design and construction principles.

2. THE INSTALLATION OF CAVITY WALL INSULATION

•Full cavity wall

Cavity is completely filled with insulation.

Advantage:
- placing is less critical
- no chance of convection streams

Disadvantage:
- insulation is in direct contact with the damp outer leaf
- certaub insulation products become damp slowly
- negative influence on the insulation capacity
- outer leaf can only dry up trhough the outside
- outer leaf may not be painted nor constructed out of vapour impermeable materials

Advised against with:
- strongly exposed outside walls (outside walls higher than 25 metres)
- outside walls of buildings in the coastal region higher than 8 metres
- all outside walls of buildings situated along the beach
- strong vapour impermeable outside walls, for instance outside walls finished with vapour impermeable paint of when using glazed facing bricks

Partial cavity wall filling

Cavity wall is not entirely filled with thermal insulation.   Advantage: - insulation is never in contact with the outer leaf - appaers on the inside of the external cavity layer in case of internal insulation - insulation is never exposed to this water of condensation - the outer leaf can dry up faster as a consequence of the ventilated cavity wall - outside wall may be painted or be made out of vapour impermeable brick   Disadvantage: - implementation demands more attention (expertise) - chance of convection stream after wrong placing In short: A perfect insulation is realised when preserving all cavity wall functions.

1. EUROWALL
2. Inner leaf
3. Internal gypsum plaster
4. Footlead
5. Concrete covering layer
6. EUROFLOOR
7. Concrete floor
8. Insulating building stone
9. Outer leaf
10. Open butt joint
11. Clip 
12. Wall tie
13. Ventilation space
14. Disengaging strip / floor

Placing

1. Glazing
2. Window
3. Vaulting
4. EUROWALL
5. Inner leaf
6. Coat of plaster
7. Joint filling
8. Metal angle section
9. Open butt joint
10. Outer leaf
11. Damming layer
12. Door and window frame

Walls under construction need to be protected from weather influences during the duration of the works. During work interruptions (at the end of the day or week, beginning of holidays,...) the walls will be temporarily covered from water infiltration.